In a conventional method for producing a ROM semiconductor device having memory cells arranged in an array, in order to determine programming or state of "1" or "0" in each of the memory cells arranged in an array in accordance with a desired purpose for use, a flash memory capable of writing data therein and reading it out therefrom is firstly formed, then "1" or "0" is written in each memory cell a user side to verify whether the program works as expected, and the program to be written in the ROM is finally determined. Then, the ROM has "1" or "0" written in each memory cell by changing an impurity concentration of a channel region, so that a ROM semiconductor device is produced.
Since the semiconductor device having the ROM is different from a semiconductor device having a flash memory in the structure of the memory part, in general they are manufactured with different production lines and each mask is separately manufactured, and each condition for the respective devices is separately set.
However, other semiconductor elements such as a sense amplifier included in the semiconductor device having a flash memory for determining an optimized state ("1" or "0") to be written in the ROM are the same as those included in the semiconductor device having the ROM of which the state is finally determined. The separate production lines similar to each other lead to a mistake of production conditions and hinders effective operations of production equipment.
In addition, separate masks for individual use are formed for formation of corresponding elements of the semiconductor device having a flash memory and the semiconductor device having the ROM identical therewith, resulting in an increase in the cost for mask, hence for the production of the semiconductor device.